Measurement limits in gravitational wave detection：the story of enhancing sensitivity

Since the first detection of gravitational waves from a binary black hole merger by laser interferometric detectors in 2015, gravitational wave astronomy has rapidly evolved into a crucial window for exploring the universe. However, gravitational wave signals are extremely weak, approaching the fundamental limits of scientific measurement. This article reviews the key milestones in gravitational wave detection, introduces the principle of laser interferometers and methods for characterizing their sensitivity, and summarizes the main noise sources limiting detector performance, including classical noise such as environmental and thermal noise, as well as quantum noise such as shot noise and radiation pressure noise. Furthermore, we discuss advanced quantum optical techniques—such as those based on squeezed states of light, quantum non-demolition measurements, and coherent feedback—that enable the standard quantum limit to be surpassed. We also introduce the concept of the fundamental quantum limit, providing a unified framework that reveals the underlying connections among various noise-reduction strategies.